Blender freezes, but no resources are maxed out
Processes like render can be separated in different parts, as you can see as a tiles. But some processes (like the smooth) can't be divided into threads to use all the processor cores. In this case one thread use only 1 CPU core: 1/4 or 1/8 (depends of how many cores in your CPU) of all CPU power. If so, CPU monitor will show that only 25% or 12% of CPU is used.